1. Field of the Invention
The invention relates to a method for manufacturing oxidic sintered nuclear fuel bodies by compacting UO.sub.2 -starting powder or a mixture of UO.sub.2 and PuO.sub.2 -starting powder which contains up to 10% by weight rare-earth oxide, especially Gd.sub.2 O.sub.3, as an additive, into blanks and subsequent densification of these blanks by a heat treatment in a sintering atmosphere with reducing action.
2. Description of the Prior Art
Such a method is known from German Published Non-Prosecuted Application No. 29 39 415 (corresponding U.S. application Ser. No. 190,981, filed Sept. 26, 1980, now U.S. Pat. No. 4,438,050). The heat treatment of the blanks is performed in this known method initially in a sintering atmosphere with oxidizing action at 800.degree. to 1,400.degree. C. for a time of 15 minutes to two hours and only then in a sintering atmosphere with reducing action at a temperature of above 1,650.degree. C. for a time of thirty minutes to four hours.
During the heat treatment in the oxidizing atmosphere, the blanks pass at the relatively low treatment temperature into an overstoichiometric state, in which the development of sintering-inhibiting phases (U, Gd)O.sub.2.+-.y) is not activated, which would permit the development of high sintering densities in the blanks only after very long sintering times.
With the known method, oxidic sintered nuclear fuel bodies are obtained which contain a rare earth element, for instance, gadolinium as a neutron poison which can burn up neutron-physically, and the sintering density of which is more than 90% of its theoretically possible density, and therefore liberate relatively few gaseous or highly volatile nuclear fission products in an operating nuclear reactor. Fuel rods which contain sintered nuclear fuel bodies obtained by known methods therefore develop at most a small overpressure in the fuel rod cladding tubes. During operation in the nuclear reactor, no shrinkage and no local overheating of these sintered nuclear fuel bodies occurs, either of which would lead to fuel rod defects.